1. Field of the Invention
The present invention relates to an exposure method in a lithography process, an exposure quantity calculating system and a manufacturing method of a semiconductor device.
2. Description of the Related Art
Recently, along with progress in size reduction technology of semiconductors, the sizes are reduced in each lithography process in the manufacture of semiconductor devices, and both size control at high precision and with low fluctuation are demanded at the same time. To satisfy the demand, it is necessary to determine the optimum exposure quantity and focus position in each mask and exposure device used in each lithography process, and this job is generally known as exposure conditioning.
During an exposure conditioning job, the manufacturing process must be stopped, and since it is a time-consuming job, it is desired to shorten the time as much as possible in consideration of production efficiency. To simplify this kind of exposure conditioning job, a method as shown in FIGS. 9 and 10 is known (for example, see Jpn. Pat. No. 3152776 (page 5, FIGS. 1 and 2)).
FIG. 9 is a block diagram of a configuration of an exposure calculating system, and FIG. 10 is a flowchart showing a method of calculating an exposure quantity.
The exposure calculating system disclosed in Jpn. Pat. No. 3152776 comprises, as shown in FIG. 9, mask size measuring unit 101 for measuring the pattern size of a mask for use in a lithography process, resist pattern size measuring unit 102 for measuring the size of a pattern formed on a resist film in the lithography process, an input unit 103 for inputting conditions about the lithography process and data about the processing lot, and a processing unit 104 for processing data sent from the mask size measuring unit 101, the resist pattern size measuring unit 102 and the input unit 103, storing the processed data in a storage 105, calculating the exposure quantity by using the data stored in the storage 105, and giving an instruction to an exposure device 106. The mask size measuring unit 101, the resist pattern size measuring unit 102, the input unit 103, and the storage 105 are connected to the processing unit 104, and the processing unit 104 is connected to the exposure device 106.
In a method of calculating an optimum exposure quantity, as shown in FIG. 10, first, an exposure curve is approximated as a straight line, a target resist pattern size is substituted by using the inclination of exposure curve (exposure correction coefficient) obtained from the exposure quantity and the exposure data accumulated, and a first exposure quantity is calculated (step S101). In succession, by using the inclination near the target resist pattern size (mask correction coefficient) in the exposure curve composed of the past exposure data, and the difference (size deviation) between the mask design size and the size of the mask to be used, a correction exposure quantity is calculated (step S102). Summing up the first exposure quantity calculated in step S101 and the correction exposure quantity calculated in step S102, a new exposure quantity is calculated (step S103).
Repeating these steps several times, the optimum exposure quantity for satisfying the target resist pattern size is calculated. Herein, data required for calculating the optimum exposure quantity include accumulated exposure data of a plurality of lots, an exposure data curve based on the exposure quantity versus resist pattern size, and the exposure correction coefficient, mask correction coefficient, size deviation, etc.
In the above-explained method of exposing a semiconductor device, between lots and between semiconductor wafers in semiconductor device manufacture, size control of high precision and with low fluctuation can be achieved. However, it requires sampling of the exposure data curve and calculating jobs of the exposure correction efficiency, mask correction efficiency, size deviation, etc. This conventional method further requires sampling of the exposure conditioning job several times. Therefore, it takes time and labor for calculating the optimum exposure condition.